Arithmetic
About 6 min · Numerical Ability · English
Time worked out from the lesson's 411 words at 150 words a minute, plus a minute for each question.
Arithmetic forms the backbone of the Numerical Ability section in SBI Clerk Prelims. These questions test your ability to apply basic mathematical concepts quickly—speed matters more than complexity at the Clerk level.
Key ideas
- Percentage is the foundation: Almost every arithmetic topic—profit/loss, interest, ratio changes—ultimately converts to percentage calculations. Master percentage first.
- Ratio thinking beats equation solving: Instead of setting up algebraic equations, think in terms of "parts" and "multipliers." A 3:5 ratio means 8 total parts—this mental model speeds up calculations.
- Work and Time are inversely proportional: If A is twice as efficient as B, A takes half the time. This inverse relationship applies to pipes/cisterns too.
- SI grows linearly, CI grows exponentially: Simple Interest adds the same amount each year. Compound Interest adds increasing amounts because interest earns interest.
- CP-SP-MP form a triangle: Cost Price → add profit margin → Selling Price. Marked Price → subtract discount → Selling Price. Most problems ask you to navigate this triangle.
Watch out for
- Adding successive percentages directly → Wrong: 10% increase then 20% increase ≠ 30% increase. Correct: Use formula a + b + ab/100 = 10 + 20 + 200/100 = 32%.
- Calculating profit% on SP instead of CP → Wrong thinking: "I sold for 120 and made 20 profit, so profit% = 20/120." Correct: Always calculate profit% on CP, so it's 20/100 = 20%.
- Confusing time taken with work done → Wrong: If A is twice as fast, A takes twice the time. Correct: A takes half the time (inverse relationship).
Quick reference
- Successive % changes: Net = a + b + (ab/100)
- Profit% = (SP − CP)/CP × 100; Discount% = (MP − SP)/MP × 100
- CI − SI for 2 years = P(R/100)²
- Combined work rate = Sum of individual rates
- Average speed for equal distances = 2ab/(a+b)
Check yourself: 3 questions
1. A shopkeeper marks his goods 40% above the cost price and allows a discount of 25% on the marked price. Find his gain or loss percent.
2. A can complete a work in 12 days and B can complete the same work in 18 days. They work together for 4 days, and then A leaves. In how many more days will B finish the remaining work?
3. In a mixture of 80 liters, the ratio of milk to water is 7:3. How many liters of water should be added to make the ratio 1:1?
This lesson is cut from the topic's note, not rewritten. Fact-checked on 18 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.
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